AATH support and test expansion for RFC-0771 Anoncred Attachement Formats

[nodlesh]

See https://github.com/hyperledger/aries-rfcs/tree/main/features/0771-anoncreds-attachments

[ianco]

This will only work with askar-anoncreds wallets, no?

Should we update the test runs to use askar-anoncreds rather than askar?

[ianco]

I'm going to put in a check - if the test requires an askar-anoncreds wallet and the agent isn't running an askar-anoncreds wallet then the test will fail.

For now I'll leave the anoncreds-specific tests out of the AcceptanceTests (so they won't get run in the github runs) and we can add them once we set our default wallet type to askar-anoncreds.